Ultrafiltration (UF) and microfiltration (MF) are increasingly being used for purification, concentration or fractionation of feed components in water and wastewater treatment, and in industrial processes. The benefits of membrane processes include lower energy requirement, much better product quality, smaller footprint and ease of operation. In addition to their well-established use in industrial separations, UF and MF processes serve as an excellent pre-treatment option for nanofiltration and reverse osmosis in water and wastewater treatment. However, these processes suffer from membrane fouling, which affects membrane performance negatively in terms of flux and separation characteristics, which in turn, results in higher capital and operating cost for a given through put and product quality. Membrane fouling could be of biological, colloidal, particulate or scaling in nature. Therefore, in addition to preventive measures, effective membrane cleaning is equally important for economic operation of UF and MF plants.
Membrane cleaning processes usually consist of removing the membrane system from service, rinsing the membrane system with high quality water, preparing a cleaning solution, heating the cleaning solution, circulating the cleaning solution at low pressure through the membranes and back into the clean-in-place (CIP) tank. The process may also include alternating periods of circulating the cleaning solution through the system and soaking the system in the cleaning solution. The system may also be rinsed and fresh cleaning solution applied as needed. Finally the system is rinsed with permeate quality water and either subjected to a second cleaning or placed back in service. In some of the hollow-fiber UF and MF membrane systems, backwashing with or without chemical is commonly practiced to control particulate and colloidal fouling. However, this method does not eliminate the thorough membrane cleaning procedure (CIP, clean-in-place) required to restore the membrane performance. Frequency of membrane cleaning as well as type of chemicals used in cleaning formulations can affect membrane life and therefore the operating cost. Therefore, improved cleaning methods and products are needed to restore the membrane performance (e.g. productivity and separation characteristics) and to extend the membrane life.